Network Display Extention
With Intel's WiDi (Wireless Display) technology built in to it latest chips and the derivatives like Apples Air Display I thought I'd have a look around for a software only solution as I was sure I had seen something like it before.
I found this:
That allows you to create additional 'virtual' screens that are shared out via VNC to additional devices so that you can extend your screen over multiple devices like an old laptop, PDA, Tablet etc.
It is not driver signed so requires a lot of messing to get it working under 7x64 but still a cool little app.
The other tech is here:
Laptop to TV with Intel® Wireless Display (WiDi)
App Store - Air Display